In the communications art, different wireline/wireless technologies—e.g. Ethernet, WiFi, 3GPP, 3GPP2, WiMAX—have evolved down distinct paths, each providing services with different characteristics. For example, WiFi is mainly deployed indoors while 3GPP provides a much larger service area outdoors. To provide better coverage and better user experience, some vendors provide proprietary dual-mode mobile terminals which allow users to access two different networks, e.g. WiFi and GSM.
Relatedly, IEEE 802.21 (Media Independent Handover, “MIH”) is a standards development directed to the enablement of handover and interoperability between heterogeneous network types including both 802 (e.g. WiFi/WiMAX) and non-802 (e.g., 3GPP) networks. A principle aim of the 802.21 standard is to provide a generic solution for intelligent handover between these technologies. FIG. 1 shows the basic MIH function which resides between the Data Link layer (Layer 2 (L2)) and the Network layer (Layer 3 (L3)) of the OSI Network Model. MIH can provide L2 handover related information, e.g., Link-up, Link-down, Link-Handover-Imminent, etc., to upper layers to facilitate L3 handover.
Wireless communication systems, generally, use a geographically-dispersed network of interconnected base stations to provide wireless connectivity to mobile nodes. The network operates according to standards and/or protocols that allow the mobile nodes to roam between the interconnected base stations via handover from base station to base station, as the mobile node's location changes. One example of a communication protocol that supports user mobility is Mobile Internet Protocol (Mobile IP), which is an Internet Engineering Task Force (IETF) protocol that allows mobile nodes to move from one network to another while maintaining a permanent IP address throughout the session that requires mobility. A mobile node that operates according to Mobile IP is assigned a permanent IP address called a home address on its home network (the assignment being for the duration of the session), and a care-of address that identifies the current location of the mobile node within a network and its subnets.
A home agent (hereafter, generally designated “HA”) stores information about mobile nodes that have a permanent home address in the home agent's network. Foreign agents (hereafter, generally designated “FA”) store information about mobile nodes that are visiting the foreign agent's network, and advertise care-of addresses to these mobile units.
Each time a mobile node moves to a different network, it acquires a new care-of address that corresponds to a target FA. In the home network, the HA associates each permanent home address of the mobile node with its current care-of address. The mobile node sends the HA a message to establish a binding between the home address and care-of address each time it changes its care-of address, using a Mobile IP protocol defined in IETF RFC 3344. When traffic is sent to the mobile node, the packets are addressed to, and initially received by the HA, and forwarded via tunneling mechanisms to the appropriate care-of address—typically the FA at the mobile node's current location.
In Version 4 of the Mobile IP protocol (sometimes designated hereafter as “MIPv4”), when a mobile node (hereafter generally designated as “MN”) enters a MIPv4 network, it searches for an FA that can act as the MN's Care of Address (CoA). Through a registration procedure initiated by the MN, a tunnel is established between the FA and the HA for that MN. All data from Correspondent Nodes (CN) destined for that MN are intercepted by the HA and forwarded over this tunnel to the current CoA. The receiving FA is then responsible for delivering the data to the MN. As described above, the Mobile IP mechanism provides a transparent solution for mobility management such that a CN need not know where the MN resides (e.g. home or roaming).
When an MN roams to a different type of access network, e.g., from a WLAN network to a 3GPP network, this is called a vertical handover. (Relatedly, if the types of networks are the same before and after the handover, this is called a horizontal handover.) Handovers can also be classified by layers, e.g. Layer 2 or Layer 3. Because a handover involves many operations, e.g., physical reconnection, protocol negotiation, reconfiguration, etc., it is inevitable that performance deterioration will occur during the handover. Among such performance issues, latencies are introduced during a handover process that include L2 disconnection detection, L2 reconnection, L3 re-connection, etc. Typically, an L3 handover occurs after an L2 handover is completed.
A timing diagram for a representative MN handover in MIPv4 is shown in FIG. 2. The timing events depicted in the figure, indicated in the figure as “ti” are defined below.                t1: L2 disconnection detection        t2: L2 connection up (e.g. power up, association)        t3: MN solicitation        t4: FA advertisement        t5: MN registration request        t6: FA processing and MN-FA authentication        t7: Registration forwarding        t8: Home Agent (HA) processing        t9: Authentication        t10: HA processing (e.g. tunnel setup)        t11: Registration reply        t12: FA processing        t13: Registration reply        t14: MN update (e.g. routing table update)        t15: Connection resumed        
Many methods have been proposed to reduce the various types of handover latencies, such as switching the order of L2/L3 handover or reducing the absolute latency value by localizing the L3 registration processing, etc. In accord with the order switching idea, a methodology called Low-latency Handover contemplates a Preregistration method wherein the MN registers with a new FA through the current FA before attaching to a new network. Hence, in that approach, the MN does not need to wait until the L2 handover is completed to start the L3 handover. Ideally, the L3 handover latency, generally t3˜t14 in FIG. 2, can be removed and therefore a quicker handover is achieved.
Alternatively, an approach called Regional Registration suggests a hierarchical architecture which alleviates the high latency of MN-HA registration and authentication by setting a regional GFA (Gateway Foreign Agent) to provide a quicker registration locally. However, all of the abovementioned algorithms are designed based on the assumption that there is only one type of interface in the MN and that the handover is between two FAs of the same interface type—i.e., a horizontal handover. For vertical handover, however, these methods are not applicable without extensive modification. Note that different access technologies typically use different authentication mechanisms.